Dishes which have been washed by machine are nowadays subject to high requirements. For example, even dishes which have been completely cleaned of food residues will not be evaluated as being perfect if, after machine dishwashing, they still have whitish marks based on water hardness or other mineral salts which, due to a lack of wetting agents, originate from dried-on water drops. In order to obtain sparkling and stain free dishes, a rinse aid is therefore used. The addition of a liquid or solid rinse aid, which can be added separately or is already present in ready-to-use form together with the detergent and/or regeneration salt (“2 in 1”, “3 in 1”, e.g. in the form of tablets or powders) ensures that the water runs off from the ware as completely as possible, so that the various surfaces at the end of the wash program are residue-free and sparkling.
Standard commercial rinse aids are mixtures e.g. of nonionic surfactants, solubility promoters, organic acids and solvents, water and optionally preservatives and fragrances. The task of the surfactants in these compositions is to influence the interfacial tension of the water in such a way that it can run off from the ware in a coherent film which is as thin as possible so that, during the subsequent drying operation, no water drops, streaks or films remain (so-called wetting action). For this reason, surfactants in rinse aids must also suppress the foam in the dishwashing machine which arises as a result of food residues. Since the rinse aids in most cases comprise acids to improve the clear-drying effect, the surfactants used must additionally be comparatively hydrolysis-insensitive toward acids.
Rinse aids are used both domestically and also in the commercial sector. In domestic dishwashers, the rinse aid is in most cases added after the prewash and cleaning operation at about 40 to 65° C. Commercial dishwashers operate with only a cleaning liquor which is renewed merely by adding the rinse aid solution from the previous washing operation. Thus, there is no complete water exchange during the entire wash program. For this reason, the rinse aid must also have a foam-suppressing action, be stable even at a steep temperature gradient from about 85 to about 35° C., and be inert toward alkali metal and active chlorine compounds.
The object of the present invention was therefore to provide nonionic surfactants in solid form for the preparation of solid laundry detergents, dishwashing detergents and cleaners, specifically of solid dishwashing detergents, in particular the so-called “2 in 1” or “3 in 1” dishwashing detergents, in the form of tablets or powders which are characterized in that they have excellent clear-rinse properties, have a foam-suppressing action even in the presence of protein soilings, are stable even at a severe temperature gradient, are inert toward alkali metal and active chlorine compounds, do not form gels upon dissolution and, in particular have solubility kinetics which permit an entrainment of the highest possible content of nonionic surfactant into the washing operation of the machine process.